Heavy metals such as lead, zinc, mercury, arsenic, silver and the like can be present in trace amounts in all types of fuels such as crude oils. The amount can range from below the analytical detection limit (0.5 μg/kg) to several thousand ppb depending on the feed source. It is desirable to remove the trace elements of these metals from crude oils.
Various methods for removing trace metal contaminants in liquid hydrocarbon feed prior to fractional distillation have been developed. One of the metal contaminants in crude oil is mercury, which is present primarily as elemental dissolved Hg(0) and particulate Hg (liquid droplets or liquid Hg adhering to sand particles). To remove existing Hg particulates or fine HgS and/or HgO crystals precipitated upon treatment of the liquid hydrocarbon, hydrocyclones and/or filters are typically used. Filtering crude oil to remove HgS and/or HgO and other Hg-containing solids is expensive and cumbersome.
In the prior art, iodide impregnated granular activated carbons have been used to remove mercury from water. U.S. Pat. No. 5,336,835 discloses the removal of mercury from liquid hydrocarbon using an adsorbent comprising an activated carbon impregnated with a reactant metal halide, with the halide being selected from the group consisting of I, Br and Cl. U.S. Pat. No. 5,202,301 discloses removing mercury from liquid hydrocarbon with an activated carbon adsorbent impregnated with a composition containing metal halide or other reducing halide. US Patent Publication No. 2010/0051553 discloses the removal of mercury from liquid streams such as non-aqueous liquid hydrocarbonaceous streams upon contact with a Hg-complexing agent for mercury to form insoluble complexes for subsequent removal.
There is still a need for improved methods for trace elements, e.g., mercury, extraction from hydrocarbons such as crude oil, wherein the heavy metals form water soluble metal complexes for subsequent removal from the crude oil by phase separation.